1. Field of the Invention
The present invention relates to washing machines, and more particularly, to a washing machine which enables simplification of a structure of a driving unit and which provides an adequate driving torque even if a small sized motor is utilized therein, and a method for controlling the same.
2. Discussion of the Related Art
In general, washing machines wash laundry by action of circulation of washing water, and a chemical action, such as detergent, and the like.
In the washing machines, there are top load type washing machines, and front load type washing machines. In the top load type washing machines, there are tub rotating type machines, and pulsator type washing machines, and in the front load type washing machines, there are drum type washing machines.
For washing and spinning, a driving unit is provided to the washing machine. The driving unit generally has an induction motor applied thereto.
The induction motor does not have a brush and commutator, and no magnets are provided to a rotor thereof. The induction motor has no burning of the brush and the commutator, and no demagnetization of the magnets, accordingly. The induction motor generates a rotation force by interaction of a rotating magnetic field generated by a current flowing through a line wound on a stator and a current induced at the rotor.
The induction motor is coupled to a washing shaft, and the washing shaft is coupled to a reduction gear unit. The washing shaft has a clutch coupled thereto for increasing/decreasing a speed of an inner tub by using a reduction gear unit.
The drum type washing machine washes laundry at a low rotation speed of the inner tub by the reduction gear in a washing cycle, and extracts water from the laundry as the inner tub spins at a higher rotation speed in a spinning cycle.
However, conventional driving units of the washing machine have several problems.
First, if the driving unit has the induction motor applied thereto, even though a unit cost of the motor can be lowered, there has been a problem in that a structure of the driving unit becomes complicated because a clutch and a speed reduction device are required additionally for regulating a rotation speed of the motor.
Second, since the driving unit moves together with devices, such as clutch, mechanical, and electrical noise increases.
Third, because a torque on the inner tub increases in proportion to the speed reduction by the reduction gear in the washing cycle, the washing cycle can be started, directly. Opposite to this, at an initial stage of spinning, there is shortage of the torque on the inner tub as the torque is not increased by the speed reduction of the reduction gear. Particularly, in a case of small sized motor, such a problem is distinctive.
Fourth, for starting the spinning cycle, the inner tub is rotated in regular/reverse directions to distribute the laundry evenly, and, then, the torque is increased to a certain level to start a spinning mode. However, this method prolongs a spinning time period due to the longer starting time period, and increases power consumption.
Fifth, the regular/reverse direction rotation of the inner tub for starting the spinning causes heavy mechanical and electrical noise.